Arrangement for objectively evaluating characteristics of gems, particularly diamonds

ABSTRACT

The arrangement includes an ellipsoidal mirror having a first focal point and a second focal point. Light is emitted from the first focal point. A gem is supported at the second focal point with such an orientation that the light emitted from the first focal point and reaching and entering the gem will be reflected by the gem towards a plane containing the first focal point and oriented normal to a line joining the focal points. The gem is surrounded and engaged by a light blocking arrangement to prevent the passage of light past such gem around the outermost portions of the gem. The light emitted from the first focal point and reflected by the gem towards such plane is measured.

United State, [111 3,867,032 Bmk SUBSTITUTE FOR MISSING xi 1 Feb. 18,1975 [54] ARRANGEMENT FOR OBJECTIVELY 3 3,794,424 2/1974 Eickhorst et al356/30 EVALUATING CHARACTERISTICS OF GEMS PARTICULARLY DIAMONDS PrimaryExaminer-Ronald L. Wibert [75] Inventor: Gernot Klaus Bruck, AssistantExaminer-Richard A. Rosenberger I Bornheim-Widdig, Germany v Attorney,Agent, or Firm-Michael S. Striker [73] Assignee: Diharo DiamantenHandels Compagnie Establishment, Mauren, Liechtenstein [.57] ABSTRACT[22] Flled: 1974 The arrangement includes an ellipsoidal mirror having[21] Appl. No.: 449,553 a first focal point and a second focal point.Light is emitted from the first focal point. A gem is supported at thesecond focal point with such an orientation that [30] Forelgn ApphcatmnPnomy Data the light emitted from the first focal point and reach- Mar.20, 1973 Germany 2313783 ing and entering the gem will be reflected bythe gem Sept. 1, 1973 Germany 2344144 towards a plane Containing thefirst focal point and I oriented normal to a line joining the focalpoints. The [52] US. Cl. 356/30 gem is surrounded and engaged by a lightblocking [51] Int. Cl. Gln 21/22 rangemem to prevent the passage of hghtpast Such [58] Field of Search 356/30, 31 gem around the outermostportions of the germ The light emitted from the first focal point andreflected by [56] References C'ted the gem towards such plane ismeasured.

UNITED STATES PATENTS r 3,740,142 6/1973 Takubo 356/30 20 Claims, 14Drawing Figures PATENTED FEB] 8 I975 SHEET 1 or 6 PATENTEDFEBISHYS SHEET3 OF 6 PMENTED Y 3.867.032

' saw w e mu llulllllimllm PATENTED FEB I 8 95 3,857, 032 SHEEI SUF 6 lFIG. 11

v 57'" nu I nm PATENIEB FEB] 8 1875 SHEET 8 OF 6 FIG. 13

ARRANGEMENT FOR OBJECTIVELY EVALUATING CHARACTERISTICS OF GEMS,PARTICULARLY DIAMONDS BACKGROUND OF THE INVENTION The invention relatesto an arrangement for the evaluation of gems, such as colored anduncolored precious and semiprecious stones, and particularly diamonds.Although the invention will be described with respect to the evaluationof characteristics of diamonds, it can also be used for the evaluationof other gems.

Several different criteria are of importance in the evaluation of cutdiamonds, namely, weight, cut, purity and color. Of thesecharacteristics only weight, as expressed in carats, can be readilyascertained in an objective manner using measuring instruments, i.e., ascale. The other characteristics are so-called subjectivecharacteristics; that is, they are subjectively assessed by eye, by anexpert, usually employing ajewelers eyepiece. Even when every attempt ismade to very strictly observe the established rules for evaluating thequality of diamonds, such as they are, the resulting evaluations ofdifferent experts may differ markedly, and not only in borderline cases.This is because of the close interrelationship of all the criteria inthe final determination of the quality of the cut stone. For example, inthe case of the brilliance offire" ofa diamond, most determinative isthe quality of the cut, after which come the purity of the stone and itscolor.

An arrangement for the evaluation of the color of cut diamonds isalready known. In this known arrange ment, the diamond is held by aholding arrangement at a level underneath the Rondist of the diamond,with the entire upper portion of the diamond exposed. Provided over theholding arrangement is a source of monochromatic light, and arrangedover the diamond is a photoelectric detector. With this arrangement thecolor of the cut diamond is measured in a certain sense, but repeatablyobtainable recurring measurement, i.e., absolute measurements, cannot beobtained with this arrangement. This is because all the light from thelight source does not actually reach and enter the diamond, and becauseall of the light reflected by the diamond does not actually reach thephotoelectric detector unit. Furthermore, the known arrangement cannotbe used to ascertain other quality data concerning the diamond.

SUMMARY OF THE INVENTION It is a general object of the invention toprovide an arrangement for evaluating cut gems, especially diamonds, inan entirely objective manner, using measuring instruments, and withoutthe need for expert subjective judgement, so that the quality data orratings ascertained for a particular stone will be the same no matterhow often the ratings for the stone are determined. In other words, itis a general object to provide a rating or evaluating arrangement whichenables the generation of objective quality data, and not merely theweight of the diamond as was already possible, but also concerning theother characteristics of the stone hitherto considered subjective.

These objects, and others which will become more understandable from thefollowing description of specific embodiments, can be met, according toone advantageous concept of the invention, by providing an arrangementfor evaluating the optical characteristics of gems, especially diamonds,comprised of an ellipsoidal mirror having a first focal point and asecond focal point, and light-emitting means operative for emittinglight from the first focal point. Gem support means holds a gem at thesecond focal point with such an orientation that light emitted from thefirst focal point and reaching and entering the gem will be reflected bythe gem towards a plane which contains the first focal point and whichis oriented normal to a line joining the two focal points of the mirror.The gem support means includes means surrounding and engaging the gemand blocking off the passage of light past'the gem around the outermostportions of the gem. Light measuring means is provided for measuring thelight emitted from the first focal pointand reflected by the gem towardssaid plane.

An ellipsoidal mirror is characterized by the fact that all light raysemitted from one of the two focal points thereof will be reflected bythe surface of the mirror and pass through the other of the two focalpoints. With the apparatus of the invention, this has the consequencethat, firstly, all of the light emitted from the first focal point willbe reflected by the mirror towards the second focal point and willaccordingly enter the gem located at such second focal point and,secondly, the portion of such entering light which is thereuponreflected out of the gem will practically in its entirety, reach thelight-measuring means. The light-measuring arrangement can for examplecomprise a plurality of photocells arranged in that plane which includesthe first focal point and which is normal to a line joining the focalpoints. Also, on the support structure beneath the gem there can beprovided photocells and possibly also a condensing lens and an aperture,such photocells receiving the light which is lost, i.e., the light whichis not reflected out of the gem in direction towards the aforementionedplane and which instead leaves the gem travelling in the oppositedirection, thereby not contributing to the brilliance" and accordinglythe quality of the gem. Loss of brilliance of this type results fromimpeprfect cut, from the presence of inclusions or flaws, and may alsoresult from absorption of light by the gem. With the arrangementaccording to theinvention, it is possible to determine the differencebetween the total light entering the gem and the total light reflectedby the gem in the desired direction, in order to determine how much orhow little-light is lost as a re sult of leaving the gem at theunderside thereof and as a result of absorption.

Advantageously according to the invention, the gem support arrangementis rotatable about an axis which passes through the second focal point,and is furthermore pivotable about such focal point. This permitsdeliberate tilting of the gem to an extent sufficient to compensate forthe small amount of measurement error which may be attributed to theincompleteness of the ellipsoidal mirror resulting from the presence ofphotocells in the aforementioned plane, for example, and to the presenceof the light source.

If a plurality of photocells are arranged in the abovedefined plane,then the measurement of the light reflected by the stone is ameasurement of the intensity of the light. To determine the colorcharacteristics of the gem, the light employed can be of successivedifferent colors of the spectrum, with the intensity of the reflectedlight being measured separately for each color. Many cut stones have toa certain extent a fluorescent character; short-wavelength lightentering the stone may produce an emission of long-wavelength light,i.e., there may occur a frequency shift in direction towards theinfrared end of the spectrum. In other words, the incidentshort-wavelength light results in a detection by the photocells of a lowefficiency situation (namely, a decrease corresponding to thefluorescence component), whereas upon a subsequent measurement usinglonger-wavelength light the photocells will detect a greater apparentefficiency with respect to the amount of light reflected, as a result ofthe fluorescence. For the total measurement of the brilliance ofthe gem,i.e., for the measurement of the gems brilliance over the entirespectrum, this fluorescence is without meaning, because all that isactually determined is the amount of light energy reflected by thestone, irrespective of whether the reflection of energy is direct or theresult of a fluorescent effect. However, when the color of the stone isdetermined, this fluorescent effect results in certain deviations ofinaccuracies, explained in greater detail with respect to specificembodiments of the invention.

This will also be the case with other embodiments of the invention, forexample, according to which use isv made of light-conducting bodies orlight-conducting elements or bundles of such elements, operative forconducting the reflected light from the above-defined plane to a lightmeasuring apparatus capable of differentiating between the individualspectral components of the light.

With the first approach mentioned above, polychromatic light is resolvedinto its spectral components by means of a spectral apparatus, e.g., amonochromator, and the individual spectral components are separately andsuccessively conducted to the first focal point of the ellipsoidalmirror in order to measure the intensity ofthe reflected light by meansofphotocells. According to the second approach mentioned, polychromaticlight is emitted from the first focal point of the mirror, and the lightreflected by the stone is conducted to a spectral apparatus andthereupon resolved into its spectral components, the intensity of suchspectral components being measured by means of photocells. This resultsin a marked simplification and shortening ofthe measurement operation,and approximates to the natural relationships, since in ordinary use thestone will be illuminated by polychromatic light and the resultingreflected light is what is perceived when subjectively determining thebrilliance and color of the stone. The abovedescribed spectral shiftresulting from the abovedescribed fluorescent effect will be measured ina manner corresponding to natural conditions.

To determine the presence offlaws or inclusions, and to quantify thecharacter of such flaws, use can be made of a laser beam, the laser beambeing parallel to the line joining the focal points of the mirror andpreferably being shiftable by means of an adjustable mirror. With suchas arrangement, the gem can be turned, by turning the gem support, andsimultaneously the laser beam can be slowly shifted in radial direction,so that a plot of the output signals of the photocells will constitute asort of spiral development of the volume of the stone, and such signalswhen plotted in graph form constitute objective information concerningthe size, position and character of the flaws.

When the volume of the stone is geometrically developed" in this mannerusing a laser beam, then it is also advantageous to support the stoneupside down,

with the pyramidal bottom part of the stone facing the light source andwith the table of the stone facing in opposite direction, use stillbeing made of the lightblocking means surrounding and engaging thestone, for example at the edge of the Rondist plane thereof. With thisapproach, the laser beam enters the stone at the pyramidal lower portionthereof. The laser beam will then emerge from the opposite side of thepyramidal body of the gem; should the beam encounter an inclusion insidethe stone, :1 portion of the beam will be dispersed, and the componentof the beam emerging out of the table face of the stone, in directionnormal to the table face, can be measured by means of photocellsprovided in the gem support structure in order to generate dataconcerning the presence and size of inclusions. This radiation emergingfrom the table face of the stone, in a direction normal to the tableface, can be condensed by means of a convergent lens and passed throughan aperture onto the photocell arrangement.

The advantage of this kind of geometric development of the volume of thestone, for the purpose of detecting and evaluating flaws, resides in thefact that the developed laser beam will not pass through the numerousfacet edge portions of the lower or back por tion of the stone, with thelight beams necessarily impinging upon the photocells and illuminatingwith stray light, which during the evaluation of the develop ment" mustsomehow be excluded from consideration, since they are not produced byflaws.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however. both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in con nection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a vertical section through afirst embodiment;

FIG. 2 shows a modification of a portion of the embodiment of FIG. 1',

FIG. 3 shows a modification of a portion of the embodiment of FIG. 1',

FIG. 4 is a diagrammatic depiction of a set-up for determining the colorofa stone using the arrangement of FIG. 1;

FIG. 5 is a diagrammatic depiction of a set-up for determining the colorof a stone using the arrangements of FIGS. 6 and 7;

FIG. 6 is a vertical section through another embodiment;

FIG. 7 is a vertical section through a further embodiment;

FIG. 8 depicts a modification of a portion of the em bodiment of FIG. 1;

FIG. 9 depicts a cut diamond as seen from above,

FIG. 10 is a depiction of the path travelled by a laser beam employed todetect flaws in a cut stone;

FIG. 11 is a graph depicting the results of a geometri cal development"of the volume of the stone being evaluated;

FIG. 12 is a graph depicting results of measurements taken to determinethe color characteristics of a stone.

using the arrangement of FIG. 8 and the method of FIG. 10;

FIG. 13 is a vertical section through a set-up for performing ageometrical development of the volume of the stone, to detect flaws; and

FIG. 14 depicts a modification of a portion of the structure shown inFIG. 13.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The arrangement shown in FIG. 1is designated generally with reference numeral 10. It is comprised of anellipsoidal housing, in turn comprised of a lower part 12, a reflectorpart 14 and a top or cap part 16, these parts being connected togetherby means of annular flanges 13, 15 and corresponding annular projections13a, 15a received in and retained by the flanges 13, 15.

The interior surface of the reflector part 14 is formed as anellipsoidal mirror 20. Light is emitted from the first or upper focalpoint 18 of the ellipsoid The emitted light originates from anon-illustrated light source, travels in direction of the arrow 39a andenters an elongated fiber-optic light-conductive element 39, from theend of which the light is emitted into the interior of the arrangement10. The end portion 40 of the fiberoptic element 39 is positioned at thefirst focal point 18 and has a radiation characteristic of l80; forexample, it may be of hemispherical configuration. Substantially all ofthe light emitted from this end portion 40 in the first focal point 18is reflected by the ellipsoidal mirror 20 towards the second focal point19; a small error is introduced inasmuch as the ellipsoidal mirror doesnot include the interior surfaces of the cap portion 16 and of the lowerhousing portion 12. However, this small error can be compensated for, ina manner described below,

The illustrated diamond, designated with numeral 21, is held in asupport 26, so positioned that the second focal point 19 of theellipsoidal mirror lies in the Rondist plane 22 of the diamond. The edge23 of the diamond 21 is surrounded and held by a suitable clo: sure, forexample an elastic sealing ring 34, in order to prevent light frompassing around the edge 23. In the embodiment of FIG. 1, the support 26is comprised of a conical or pyramidal chamber into which the lowerportion 35 of the diamond 21 projects in which there is provided aplurality of photocells 36 so arranged that they lie adjacent to andfacing the surface of the lower portion 35 of the diamond 21. Thesupport 26 is provided at its lower end with a socket 28 into which canbe inserted the output shaft 29 of a non-illustrated drive motor, torotate the support 26 in the direction of the arrow 32. The lowerhousing portion 12 is provided with a cover plate 24 which merges into acentral portion 25 the inner surface of which is a portion of aspherical surface. The diamond support 26 is provided with acomplementary portion 27, the outer surface of which is a portion of aspherical surface. The portion 27 fits in the portion 25, so as to forma ball-type joint, permitting movement of the support 26 in thedirection of the double-headed arrow 31. Specifically, the diamondsupport 26 can be pivoted about the center of the sperical surfaces ofportions 25, 27, by means of the shaft 29. The shaft 29 passes throughan opening 30 in the housing portion 12 large enough to permit asubstantial degree of such pivoting movement.

Reference numeral 17a designates a plane which 'is oriented normal tothe line '17 which connects together I into place, and light is emittedfrom the end portion 40 of the fiber-optic element 39.

This light is practically completely reflected from all sides by theellipsoidal mirror 20 into the upper portion of the diamond 21. In thecase of an ideal diamond, allthe light will be reflected back from 'thediamond and onto the photocells 37; that is, in the case of an idealdiamond none of the light originating from member 39 will pass throughthe diamond 21 and emerge from out the lower portion thereof to impingeupon the photocells 36, and none of the'light will be absorbed by thediamond. The greater the output from the photocells 36 (i.e., thegreater the amount of light incident thereon), the worse must beconsidered the brilliance ofthe diamond 21, any such poorness of qualitybeing essentially attributable to imperfect cutting or the presence ofinclusions or faults in the body'of the diamond. Furthermore, thedifference between the light emitted from the member 39 and the totallight indicent upon the photocells 36 and 37, constitutes an indicationof the amount of light absorbed by the diamond.

A small measurement error arises, due to the fact that the innerellipsoidal surface of the cap portion 16 does not participate in thereflection of light emitted from fiber-optic element 39. However, thismeasurment error can be eliminated by pivoting and rotating the support26 holding the diamond 21. However, this error, represented in FIG. 1 bythe angle a, is extremely small; this is because in practice use can bemade of an ellipsoidal shape whose cross-section is not of thebreadth ofthe ellipse shown in FIG. 1, which was se-. lected quite broad forclarity of illustration.

The output terminals of the photocells 36 located'in the movable support26 can be connected to mercury contacts, to ensure a low-losstransmission of the output signals of the photocells.

Care must be taken to ensure that the photocells 37 are not directlyexposed to the light transmitted by the fiber-optic element 39.

It should be noted here that in the present description the expressionphotocell is employed in the broadest possible sense and is to beunderstood as signifying any light-sensitive or light-responsive elementor device capable of generating a signal or indication of the intensityor amount of incident light, in addition to such elements and devices asproduce a light-dependent electrical current or voltage or vary themagnitude of such current or voltage (e.g., a photoresistor).

As will be-understood by persons skilled in the art, with thearrangement of FIG. 1, a central vertical beam oflight incident upon theupper portion of the diamond 21 will pass right through the diamond andemerge from the lower vertex thereof. In order to eliminate theresulting measurement error, use can be made of the somewhat modifiedarrangement shown in FIG. 2.

In FIG. 2 components corresponding to those of FIG. 1 are designated bythe same reference numeral, but primed. These need not be describedagain.

In the arrangement of FIG. 2, use is made of a boxshaped support 26.Provided in the interior of support 26' are photocells 36' correspondingto photocells 36 of FIG. 1. However, there is additionally provided aphotocell 36a located to receive the just-mentioned beam of light whichpasses through the central portion of the diamond. Separate detection ofthis beam oflight makes it possible to add or subtract from the variousmeasured and computed amounts of light an amount corresponding to thisthrough-passing central light beam, thereby eliminating the measurementerror referred to.

FIG. 3 depicts one light source which can be employed. It includes alaser 45, the laser beam 46 of which is deflected by a mirror 44 intothe interior of the arrangement 10. The mirror 44 is advantageouslymounted on a small pipe-shaped member 48 secured to a supportingstructure 43, there being mounted at the lower end of member 48 a groundglass sphere 47. The sphere 47 emits the laser light over an angle of180 and will, as was the case with the end portion 40 in FIG. 1, bepositioned coincident with the focal point 18 of the ellipsoidal mirror20.

The manner in which the apparatus of FIG. 1 is used to perform thechromatic evaluation of the diamond will be explained with reference toFIG. 4.

Polychromatic light from a light source 390 is broken up into itsconsitutent color components by passage through a spectral apparatus380, for example, a monochromator, and the individual color componentsare individually led into the interior of the apparatus 10 by means ofthe fiber-optic element 39. Use is made of an ammeter of voltmeter 38 tomeasure the electrical signal developed across the outputs of thephotocells 37 in response to the reflection back upon them of themonochromatic light directed towards the diamond. The photocells 37,which will be arranged so as to form as nearly as possible an unborkenphotoresponsive surface, may each have a pair of output terminals, withthe individual photocells being all connected together in series or inparallel, depending for example upon whether the photocells generate alightdependent voltage or a light-dependent current. In this way, themeasurements explained with reference to FIGS. 1 and 2 can be performedfor each of the spectral components separately. This will be explainedstill further with respect to FIG. 12.

Another embodiment of the invention is depicted in FIGS. 5-7, theoperation of this embodiment being explained with reference to FIG. 5.Components corresponding to those shown in FIGS. 1 and 5 are designatedwith the same reference numerals, but with the addition of a doubleprime.

Polychromatic light is emitted into the interior of the apparatus from alight source 39a. The light reflected back from the diamond impingesupon a light conducting arrangement 371-375, and is conducted to aspectral apparatus 380" which resolves the light into its constituentcolor components, which are then individually measured by means ofnon-illustrated photocells provided in the apparatus 380". Theelectrical output of the plurality of photocells is measured by anammeter or voltmeter 381".

According to this approach, which will be explained further with respectto FIGS. 6 and 7, in a single measuring operation, corresponding to thenatural relationships, polychromatic light is emitted from the firstfocal point ofthe ellipsoidal mirror, and the light impinging upon andreflected back from the precious stone is resolved into its constituentcolor components and measured. The results of the measurementsautomatically imitate the natural action of the earlier-describedfluorescent effect, although it is of course possible to also separatelymeasure the extent of such fluorescent effect.

In the structure shown in FIG. 6, the photocells 37 of FIG. 1 arereplaced by a relatively thick bundle 371 of light-conducting elements,for example glass or fiberoptic elements.

FIG. 6 depicts a modified gem support 126 in the form of a generallyannular body provided with an annular portion 127 whose outer surface isspherical and cooperates with a complementary spherical surface of acentral portion of the cover plate 124 of the lower housing part 12" ofthe apparatus 10". The gem support 126 is provided at the lower end ofan apron portion 132 with a circle of radially extending gear teeth,cooperating with a worm-gear drive 130 fixedly mounted on the apparatus10 and operative for rotating the gem support 126 about its verticalcentral axis. The photocells 136 are arranged in the interior of thebox-shaped member 128, member 128 being rigidly mounted on a shaft 129.The box-shaped unit 128 is pivotable in the direction of the double-headarrow 131 together with the rest of the gem support 126, by reason ofthe spherical configuration of the facing surfaces of portions 127 and125. The outputs of the plurality of photocells 136 can be connected byleads or other suitable means to a suitable measuring device.

The gem support l26 is provided at the upper surface thereof with arecess 138 accommodating two removable thin sheet-metal or plastic disks139. These are provided with central openings 140 and serve to encircleand engage the gem above and below the Rondist edge thereof, as clearlyshown in FIG. 6. Depending upon the size of the stone, use will be madeof different ones of a plurality of such disks 139, having centralopenings of different respective diameters. The facing surfaces boundingthe annular gaps 141 can be coated with an antifriction layer, forexample, tetrafluoroethylene, to reduce friction. With this embodiment,the diamond 21 together with the rotatable support 126, driven by theworm gear 130, turns, the boxshaped unit 128 turning therewith, and thewhole assembly being pivotable. (See FIG. 13 for an illustration of thegem support assembly in pivoted position.)

Whereas in the construction of FIG. 6 a realtively thick bundleof lighggonductivemelgments 37l is employ'ed'theconstruction of FIG. 7 mafis'dowith far fewer. In the FIG. 7 construction, there is provided in theplane l7a", oriented normal to the line l7"con necting together the twofocal points of the ellipsoidal mirror, an annular condensing lens 372which condenses the light reflected back from the gem and focusses suchreflected light onto an associated focal ring 374. Use can accordinglybe made of a relatively thin ring of light-conducting elements 375having ends positioned coincident with such focal ring, theselightconducting elements conducting the focussed light to the spectralapparatus or monochromator 380'. Other lens systems or lenses can beemployed, for example, a lens having an eccentric focal point and a borethrough which can pass the light-emitting lightconductive element orbundle of elements 39".

In FIG. 7 there is depicted in dash-dot lines a further possibility,namely the use of an annular parabolic mirror 373, instead of theannular condensing lens 372. The annular parabolic mirror 373 would havea focal ring substantially coincident with the ends of thelightconducting elements 375.

Reference will be made to FIG. 12, to describe the manner in which theoutput signals of the photocells of the arrangements of FIGS. 1-4 areemployed to determine the color, color intensity and color absorption ofthe diamond. Either a spectral apparatus is connected to the output ofthe light source (see source 390 and apparatus 380 in FIG. 4), or use ismade of an adjustable laser 45 (FIG. 3), and the diamond is illuminatedby monochromatic light in the color sequence of the spectrum, fromultraviolet, to blue, to green, to yellow, to red, to infrared. Theoutput signals of the photocells 37 are continuously measured duringthis continuous change of color, and the results are plotted in the formof the curve 73 of FIG. 12. The abscissa 71 represents the wavelengthsof the light in nanometers (I ultraviolet; II violet; Ill blue; IVgreen; V yellow; VI red; and VII infrared). The ordinate 70 representsthe light transmission. Also depicted in FIG. 12 is the standard colortransmission curve 72 for adiamond of the highest quality. The locationsof the dips and peaks of the curve 73 relative to the wavelengths of thelight and the corresponding colors indicated along the abscissa 71,constitute objective data concerning the color and color nuances of thediamond, its color being the color complementary to the color indicatedalong abscissa 71, and the magnitude of the transmission differencesbetween the standard color transmission curve 72 and the measurementcurve 73 constituting objective data concerning the intensity of thecolor of the diamond. The integral of the difference between the curves,taken with respect to wavelength, and corresponding to the sum of areas74 and 74, constitutes a total measure of the color characteristics ofthe diamond being evaluated in comparison to those of a standarddiamond.

To determine the presence of inclusions or flaws in the diamond 21, andto ascertain their character and size, use can be made of thearrangement shown in FIG. 8, in conjunction with the apparatuses ofFIGS. 13.

The cap portion 16 is provided with a slit-like opening 38 through whichpasses a small pipe-like element 48' carrying a mirror 44' whichdeflects the laser beam 46. The length of the slit-shaped opening 38 isapproximately equal to the radius of the largest diamond 21 to beevaluated. Also, in order to provide a corresponding slit-like opening42' in the arrangement of photocells 37 (FIG. 8), a segment of thephotocell arrangement is removable (this segment being designated bynumeral 41 in FIG. 1) The pipe-like member 48' in this embodiment (FIG.8) is not provided at its lower end with a glass sphere such as sphere47 of FIG. 3.

In the embodiment of FIG. 8, the pipe-like member 48' with thedeflecting mirror 44' thereon, can be shifted in radial direction, asindicated by the doubleheaded arrow 49, with the laser beam 46accordingly '10 being likewise shifted in radial. direction. Ifsimultaneously therewith the diamond 21 is turned in the direction ofthearrow 32 in FIG. 1, then by measuring the output signals of thephotocells there is achieved a sort of spiral-shaped geometricaldevelopment" of the volume of the diamond 21, indicated in FIG. 10 bymeans of a broken spiral line 56. FIG. 11 depicts an example of theresults of such a development." Plotted along the abscissa of the graphin FIG. 11 is number of the turn of the spiral, for example, the numbers1,2, 3 designating the first, second and third turns ofthe spiral line56; intermediate thesuccessive integers along'the abscissa areindications of the angle of rotation, relative to apreselected-reference orientation. Plotted along the ordinate in FIG. 11is the magnitude of the output signal of the photocell arrangement 36.

The diamond 21 depicted in FIGS. 9 and 10 contains two inclusions57, 60.The small inclusion 60, on, account of the dispersion of the laser beam46' which the inclusion 60 effects, appears-in the graph of FIG. 11 onlyin between the third and fourth turns of the spiral path, for example,and at angular orientation of about 270, asa jump in the curve. Thelarge iclusion 57 appears as several jumps 57, 57", 57", 57" in thecurve, in the third through eighth turns of the spiral beam path, at anangular orientation of about 180, and increasing in magnitude and thendecreasing in magnitude. Thus, a single jump 60' in the curve of FIG. 11indicates the presence of a small inclusion, whereas a plurality ofsuccessive jumps 57', 57", 57", 57"" indicates the presence of a largeinclusion. The intensity of the light dispersion caused by the inclusioncan be deduced from the magnitude of the jump in the curve of FIG. 11,and provides in addition informationupon which may be based adetermination of the type of inclusion, i.e., whether a gaseousinclusion, or a bodily inclusion (impurity).

Instead of performing this kind of spiral geometric development of thevolume of the diamond, it is possible to perform other suchdevelopments", for example, a zig-zagging back-and-forth development, byswinging the diamond back and forth in the direction of thedouble-headed arrow 31 of FIG.-1, but in a plane prependicular to thepicture plane of FIG. 1, while simultaneously effecting radial shiftingof the lser beam 46 in the manner described above.

A variation of such development of the diamond, for the purpose ofdetermining the presence of inclusions or flaws, will be explained withreference to FIG. 13. Here, use is made of a gem support 126 like thegem support 126 of FIG. 1, with the laer beam arrangement 44", 45", 46"of FIG. 8 being shown here only diagrammatically. The parts of thesupport 126 in FIG. 13 corresponding to those of FIG. 6 are identifiedwith the same reference numerals, primed. In contrast to the set-up ofFIG. 8, in FIG. 13 the diamond is supported by the earlier-describeddisk arrangement 139' in upside down position. The laser beam 46'emitted by the laser 45 is reflected by the mirror 44 into the diamond21, and in the case of a perfect or ideal diamond the beam 46" will inits entirety be reflected out of the diamond and emerge from the upperportion thereof (as viewed in FIG. 13) as a beam 52. However, if thediamond contains inclusions, then the laser beam will to some extent bedispersed within the diamond, resulting in the emission from the face ofthe diamond 21 of parallel rays 151, the intensity of which is measuredby means of the photocells 136' in the support 126'. These rays emittedfrom the diamond face 150 provide a further way of measuring ordetermining the presence of inclusions in the diamond 21, and can beused in conjunction with a geometric development" of the diamond 21 suchas explained with reference to FIGS. 8-11.

In order to achieve the desired total reflection of the incident laserbeam from the diamond face 150, the aforedescribed geometricdevelopment" of the volume of the diamond 21 by pivoting and rotation ofthe diamond support 126' can be preprogrammed, by experimentallydetermining the optimum angle of incidence of the laser beam 46" nearthelower vertex of the diamond 21 and near the Rondist plane (22 in FIG.1); then, the already described geometric development" of the volume ofthe diamond can be performed relative to this optimum angle ofincidence.

Furthermore, it is possible to increase the range of angles within whichthe desired total reflection by the gem occurs, by inserting the geminto a fluid of high refractive index during the determination ofthepresence of flaws or inclusions in the gem. In this way, the angle ofrefraction is decreased with the entry of the laser beam into the stone.

FlG. l4 depicts a modification according to which there is providedbeneath the daimond a convergent lens 152 which condenses the parallelrays 151 emitted from the lower face of the diamond (as viewed in FIG.14) and guides the. light through an aperture member 153 to thephotocells 136'. The arrangement is otherwise the same as described withrespect to other em bodiments above, and makes use of a box-shapedcompartment 128" mounted for pivoting movement but rotatable with theillustrated drive shaft.

it will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofconstructions differing from the types described above.

While the invention has been illustrated and described as embodied in anarrangement for evaluating the characteristics ofa precious stone, it isnot intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any wayfrom the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for vari' ous applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:

1. An arrangement for evaluating the optical characteristics of gems,especially diamonds, comprising, in combination, an ellipsoidal mirrorhaving a first focal point and a second focal point; light-emittingmeans for emitting light from said first focal point; gem support meansfor holding a gem at said second focal point with such an orientationthat light emitted from said first focal point and reaching and enteringthe gem will be reflected by the gem towards a plane containing saidfirst focal point and oriented normal to a line joining said focalpoints, said gem support means including means surrounding and engagingthe gem and blocking off the passage oflight past such gem around theoutermost portions of the gem; and light-measuring means for measuringthe light emitted from said first focal point and reflected by such gemtowards said plane.

2. An arrangement as defined in claim 1, wherein said light-measuringmeans comprises a plurality of photocells arranged in said plane andoriented to receive light emitted from said first focal point andreflected by such gem towards said plane.

3. An arrangement as defined in claim 1. and further includinglight-measuring means comprised of lightsensitive means so positionedrelative to said gem support means as to be located to that side of thesupported gem which is opposite to the side thereof which faces saidplane and operative for measuring the amount of light emitted from saidfirst focal point which penetrates the gem and emerges from such opposite side thereof.

4. An arrangement as defined in claim 3, wherein said light-measuringmeans includes condensing lens means for condensing onto saidlight-sensitive means light penetrating the gem and emerging from suchopposite side.

5. An arrangement as defined in claim 3, wherein said light-measuringmeans includes a member provided with an aperture so positioned relativeto said gem support means that light penetrating a gem supported by saidgem support and emerging from such opposite side must pass through saidaperture to reach said light-sensitive means.

6. An arrangement as defined in claim 5, wherein said light-measuringmeans includes condensing lens means for condensing onto saidlight-sensitive means light penetrating the gem and emerging from suchopposite side.

7. An arrangement as defined in claim 1, wherein said gem support meansis rotatable about said second focal point and furthermore is pivotableabout said second focal point.

8. An arrangement as defined in claim 7, wherein said gem has a Rhondistplane and wherein said gem support means comprises a chamber in whichsiad light-sensitive means is positioned, said light-sensitive meansbeing rotatable and pivotable with said gem support means, and whereinsaid gem support means comprises two centrally apertured membersoriented and positioned to surround and releasably engage a gem beingsupported by said support means above and below the edge of the Rondistplane of the gem.

9. An arrangement as defined in claim 8, wherein said centrallyapertured members are removable, and including a plurality of additionalcentrally apertured members having central apertures of different sizesto accommodate gems of different sizes.

10. An arrangement as defined in claim 7, wherein said gem support meanscomprises a gem-engaging first portion having an outer spherical surfaceand a second portion having a complementary inner spherical surface,said first portion being mounted in said second portion so as to permitboth rotational and pivoting movement of said first portion relative tosaid second portion.

11. An arrangement as defined in claim 1, wherein said light-measuringmeans comprises a light measuring instrument for separately measuringthe spectral components of light, and light-conducting means operativefor conducting light from said plane to said light measuring instrument.

12. An arrangement as defined in claim 11, wherein said light-conductingmeans comprises condensing lens means operative for focussing the lightreflected into said plane onto a second plane, and means fortransmitting the focussed light from such second plane to said lightmeasurement instrument.

13. An arrangement as defined in claim 11, wherein said light-conductingmeans comprises focussing mirror means operative for focussing the lightreflected into said plane onto a second plane, and means fortransmitting the focussed light from such second plane to said lightmeasuring instrument.

14. An arrangement as defined in claim 11, wherein said light measuringinstrument comprises means for resolving light into its spectralcomponents and for separately measuring the intensity of suchcomponents.

15. An arrangement as defined in claim 11, wherein said light measuringinstrument comprises photosensitive means operative for converting lightincident thereupon into electrical signals, and electrical measuringmeans operative for indicating the intensity of the light by indicatingthe strength of such electrical signals.

16. An arrangement as defined in claim 1, wherein said light-emittingmeans comprises a remotely located source of light and light-conductingmeans having a first end connected to said source to receive light andhaving a second end located at said first focal point to emit light andhaving a radiating character of 17. An arrangement as defined in claim1, wherein said light-emitting means comprises a laser arrangementoperative for emitting from said first focal point a laser beam.

18. An arrangement as defined in claim [7, wherein said light-emittingmeans further comprises deflecting mirror means operative for deflectingthe laser beam of said laser beam arrangement to cause such beam totravel in direction parallel to the line joining said focal points.

19. An arrangement as defined in claim 17, wherein said light-emittingmeans comprises a ground glass sphere located'at said first focal point,said laser beam being oriented to intersect said first focal point.

20. An arrangement as defined in claim 17, wherein said light-emittingmeans comprises a ground glass hemisphere located at said first focalpoint, said laser beam being oriented to intersect said first focalpoint. l

1. An arrangement for evaluating the optical characteristics of gems,especially diamonds, comprising, in combination, an ellipsoidal mirrorhaving a first focal point and a second focal point; light-emittingmeans for emitting light from said first focal point; gem support meansfor holding a gem at said second focal point with such an orientationthat light emitted from said first focal point and reaching and enteringthe gem will be reflected by the gem towards a plane containing saidfirst focal point and oriented normal to a line joining said focalpoints, said gem support means including means surrounding and engagingthe gem and blocking off the passage of light past such gem around theoutermost portions of the gem; and light-measuring means for measuringthe light emitted from said first focal point and reflected by such gemtowards said plane.
 2. An arrangement as defined in claim 1, whereinsaid light-measuring means comprises a plurality of photocells arrangedIn said plane and oriented to receive light emitted from said firstfocal point and reflected by such gem towards said plane.
 3. Anarrangement as defined in claim 1, and further including light-measuringmeans comprised of light-sensitive means so positioned relative to saidgem support means as to be located to that side of the supported gemwhich is opposite to the side thereof which faces said plane andoperative for measuring the amount of light emitted from said firstfocal point which penetrates the gem and emerges from such opposite sidethereof.
 4. An arrangement as defined in claim 3, wherein saidlight-measuring means includes condensing lens means for condensing ontosaid light-sensitive means light penetrating the gem and emerging fromsuch opposite side.
 5. An arrangement as defined in claim 3, whereinsaid light-measuring means includes a member provided with an apertureso positioned relative to said gem support means that light penetratinga gem supported by said gem support and emerging from such opposite sidemust pass through said aperture to reach said light-sensitive means. 6.An arrangement as defined in claim 5, wherein said light-measuring meansincludes condensing lens means for condensing onto said light-sensitivemeans light penetrating the gem and emerging from such opposite side. 7.An arrangement as defined in claim 1, wherein said gem support means isrotatable about said second focal point and furthermore is pivotableabout said second focal point.
 8. An arrangement as defined in claim 7,wherein said gem has a Rhondist plane and wherein said gem support meanscomprises a chamber in which siad light-sensitive means is positioned,said light-sensitive means being rotatable and pivotable with said gemsupport means, and wherein said gem support means comprises twocentrally apertured members oriented and positioned to surround andreleasably engage a gem being supported by said support means above andbelow the edge of the Rondist plane of the gem.
 9. An arrangement asdefined in claim 8, wherein said centrally apertured members areremovable, and including a plurality of additional centrally aperturedmembers having central apertures of different sizes to accommodate gemsof different sizes.
 10. An arrangement as defined in claim 7, whereinsaid gem support means comprises a gem-engaging first portion having anouter spherical surface and a second portion having a complementaryinner spherical surface, said first portion being mounted in said secondportion so as to permit both rotational and pivoting movement of saidfirst portion relative to said second portion.
 11. An arrangement asdefined in claim 1, wherein said light-measuring means comprises a lightmeasuring instrument for separately measuring the spectral components oflight, and light-conducting means operative for conducting light fromsaid plane to said light measuring instrument.
 12. An arrangement asdefined in claim 11, wherein said light-conducting means comprisescondensing lens means operative for focussing the light reflected intosaid plane onto a second plane, and means for transmitting the focussedlight from such second plane to said light measurement instrument. 13.An arrangement as defined in claim 11, wherein said light-conductingmeans comprises focussing mirror means operative for focussing the lightreflected into said plane onto a second plane, and means fortransmitting the focussed light from such second plane to said lightmeasuring instrument.
 14. An arrangement as defined in claim 11, whereinsaid light measuring instrument comprises means for resolving light intoits spectral components and for separately measuring the intensity ofsuch components.
 15. An arrangement as defined in claim 11, wherein saidlight measuring instrument comprises photosensitive means operative forconverting light incident thereupon into electrical signals, andelectrical measuring means operative for indicating the Intensity of thelight by indicating the strength of such electrical signals.
 16. Anarrangement as defined in claim 1, wherein said light-emitting meanscomprises a remotely located source of light and light-conducting meanshaving a first end connected to said source to receive light and havinga second end located at said first focal point to emit light and havinga radiating character of 180* .
 17. An arrangement as defined in claim1, wherein said light-emitting means comprises a laser arrangementoperative for emitting from said first focal point a laser beam.
 18. Anarrangement as defined in claim 17, wherein said light-emitting meansfurther comprises deflecting mirror means operative for deflecting thelaser beam of said laser beam arrangement to cause such beam to travelin direction parallel to the line joining said focal points.
 19. Anarrangement as defined in claim 17, wherein said light-emitting meanscomprises a ground glass sphere located at said first focal point, saidlaser beam being oriented to intersect said first focal point.
 20. Anarrangement as defined in claim 17, wherein said light-emitting meanscomprises a ground glass hemisphere located at said first focal point,said laser beam being oriented to intersect said first focal point.